Diffusion transfer multicolor films are well known in the art. U.S. Pat. No. 2,983,606 discloses a subtractive color film which employs red-sensitive, green-sensitive and blue-sensitive silver halide layers having associated therewith, respectively, cyan, magenta and yellow dye developers. In such films, oxidation of the dye developers in exposed areas and consequent immobilization thereof has provided the mechanism for obtaining imagewise distribution of unoxidized, diffusible cyan, magenta and yellow dye developers which are transferred by diffusion to an image-receiving layer. While a dye developer itself may develop exposed silver halide, in practice the dye developer process has utilized a colorless developing agent, sometimes referred to as an "auxiliary" developer, a "messenger" developer or an "electron transfer agent", which developing agent develops the exposed silver halide. The oxidized developing agent then participates in a redox reaction with the dye developer thereby oxidizing and immobilizing the dye developer in imagewise fashion. A well known messenger developer has been 4'-methylphenylhydroquinone (MPHQ). Commercial diffusion transfer photographic films of Polaroid Corporation including Polacolor SX-70, Time Zero and 600 have used cyan, magenta, and yellow dye developers.
U.S. Pat. Nos. 3,719,489 and 4,098,783 disclose diffusion transfer processes wherein a diffusible image dye is released from an immobile precursor by silver-initiated cleavage of certain sulfur-nitrogen containing compounds, preferably a cyclic 1,3-sulfur nitrogen ring system, and most preferably a thiazolidine compound. For convenience, these compounds may be referred to as "image dye-releasing thiazolidines". The same release mechanism is used for all three image dyes, and, as will be readily apparent, the image dye-forming system is not redox controlled.
In general, proposals to form subtractive multicolor diffusion transfer images have contemplated use of the same type of reaction to provide the requisite image-wise distributions of diffusible cyan, magenta and yellow image dyes. An exception is found in U.S. Pat. No. 3,345,163. While the preferred embodiment of said patent is the use of cyan, magenta and yellow dye developers as in Polacolor film, there is a proposal (col. 10, line 39 et seq.) to use a different reaction to control each image dye; more specifically, a proposed combination would use a tanning developer to control the cyan image dye, a coupling developer to control a magenta coupling image dye, the yellow image dye being a dye developer. In each instance, transfer of the image dye occurs where the respective developing agent was not oxidized and the image dye is diffusible unless its transfer is prevented.
Another proposal to use two different image dye control mechanisms in one film is found in U.S. Pat. No. 3,585,028. This patent proposes to use a mobile (diffusible) dye developer and an immobile (non-diffusible) image dye precursor which releases a diffusible dye following oxidation and ring-closure. In Example 1, such a combination is used to obtain a neutral image by transfer of a cyan dye developer and a "reddish" dye developer released by ring-closure, using a single silver halide emulsion layer. In Example 2 of this patent, a yellow image is obtained by transfer of a yellow dye released by oxidation of such a ring-closing precursor in addition to a yellow dye developer, again using a single silver halide emulsion layer. In each instance, oxidation of the ring-closing image dye precursor is effected as the result of development of a silver complex transferred to a nuclei layer and subsequent cross-oxidation by the oxidized form of a non-diffusible developing agent.
Another technique which utilizes two different imaging mechanisms, namely dye developers and image dye-releasing thiazolidines, is described and claimed in U.S. Pat. No. 4,740,448. According to this process the image dye positioned the greatest distance from the image-receiving layer is a dye developer and the image dye positioned closest to the image-receiving layer is provided by an image dye-releasing thiazolidine. The other image dye-providing material may be either a dye developer or an image dye-releasing thiazolidine.
In multicolor dye developer transfer processes, it has been recognized that, for example, less magenta density may be present in the transfer image than one would have predicted where there has been blue exposure but no green exposure, i.e., some magenta dye developer did not transfer even though there was no exposed green-sensitive silver halide to control its transfer. This problem is sometimes referred to as "magenta dropoff" and is believed to be the result of oxidation of the magenta dye developer as a result of the development of exposed blue-sensitive silver halide (rather than green-sensitive silver halide), the magenta dye developer being oxidized either directly or by an electron transfer redox reaction with oxidized messenger developer oxidized by exposed blue-sensitive silver halide. This undesired reaction is, at least in major part, because the magenta dye developer has to diffuse through the blue-sensitive silver halide layer to reach the image-receiving layer. In addition, the possibility has been recognized that yellow dye developer may be immobilized by development of green-sensitive silver halide, giving a different kind of crosstalk resulting in reduced yellow transfer density and increased magenta transfer density. Analogous situations may occur between the magenta and cyan dye developers. Such undesired interactions reduce color saturation and color separation and accuracy in the final image.
The photographic system taught by U.S. Pat. No. 4,740,448 reduces substantially the problem of crosstalk between adjacent silver halide emulsion layers in the formation of their respective imagewise distributions of diffusible image dyes. However, this phenomenon continues to occur in multicolor diffusion transfer photographic films such as those which utilize dye developers to provide the requisite imagewise distributions of diffusible cyan, magenta and yellow image dyes and also may occur to some extent in films which utilize dye developers together with thiazolidine image dye-providing materials dependent upon the particular photographic materials employed. It would be desirable to provide a multicolor diffusion transfer photographic film wherein such undesired interactions can be reduced substantially or virtually eliminated.